In the handling of sheet material such as is used for building construction, it has been common in recent times to provide a portable sheet bending brake wherein sheet material is clamped between an anvil member and a clamping surface and a bending member is hinged for bending the sheet material about the anvil member. Typical sheet bending brakes are disclosed in U.S. Pat. Nos. 3,161,223, 3,481,174, 3,482,427, 3,559,444, 3,817,075 and 4,240,279.
As shown, for example, in the aforementioned U.S. Pat. Nos. 3,161,223, 3,559,444, 3,817,075 and 4,240,279, the anvil member is clamped in position by means of a backing plate that has inclined cams underlying a portion of the fixed frame so that when the plate is moved longitudinally by a hand lever, the cams are moved into and out of position clamping and unclamping the backing plate.
In the aforementioned U.S. Pat. Nos. 3,481,174 and 3,482,427, the anvil is supported by pivoted bars that, in turn, are connected by links to a handle that is pivoted on the frame of the brake so that rotation of the handle moves the bars and, in turn, the anvil into and out of clamping position.
It has also heretofore been suggested that eccentric cams be utilized for moving the anvil member into and out of position as shown, for example, in U.S. Pat. Nos. 3,383,899, 4,092,841 and 4,081,986.
One of the problems with prior sheet bending brakes utilizing eccentric cams is that of adjusting the cams on the shaft. Thus, it is common to provide some type of clamp for holding the cams in position. Any such arrangement results in difficulty in adjustment and also the tendency of the clamp arrangement to loosen resulting in a loss of adjustment.
In one arrangement, the cams are adjustably mounted by bolts which can be loosened to permit rotation of the cams about the shaft. Such an arrangement operates satisfactorily but is subject to loss of adjustment in use necessitating frequent adjustment.
In U.S. Pat. No. 4,494,397 the shaft and eccentric cams are provided with circumferentially spaced teeth extending axially so that the cams are locked in any adjusted position. The position of a cam can be adjusted by moving the cam axially relative to the shaft to disengage the teeth on the cam from the teeth on the shaft, rotating the cam to the desired adjusted position and moving the cam axially to reengage the teeth.
Among the objectives of the present invention are to provide a portable sheet bending brake incorporating a novel and an inexpensive construction for adjusting and accommodating to workpieces of different thickness which is low in cost and can be adjusted without the use of tools.
In accordance with the invention, the sheet bending brake has cam support shaft is supported on the frame members by plastic bearings fixed in openings on the frame members and having tapered sides such that when the handle is operated to rotate the cams, the cam support shaft is shifted vertically and wedges against the tapered surfaces of the openings of the plastic members. The wedging action accommodates variations in the thickness of the workpiece and locks the cams holding the anvil against the clamping surface.